Vanadium-containing residual fuels modified with calcium hypochlorite



June 13, 1961 MITCHELL ET AL VANADIUM-CONTAINING RESIDUAL FUELS MODIFIED WITH CALCIUM HYPOCHLORITE Filed Feb. 9, 1959 ware Filed Feb. 9, 1959, Ser. N0. 791,938 Claims. (Cl. 60-39.02)

This invention relates to vanadium-containing petroleum fuels. More particularly, it is concerned with rendering non-corrosive those residual fuels which contain such an amount of vanadium as normally to yield a corrosive vanadium-containing ash upon combustion.

It has been observed that when a residual type fuel oil containing substantial amounts of vanadium is burned in furnaces, boilers and gas turbines, the ash resulting from combustion of the fuel oil is highly corrosive to materials of construction at elevated temperatures and attacks such parts as boiler tubes, hangers, turbine blades and the like. These effects are particularly noticeable in gas turbines. Large gas turbines show promise of becoming an important type of industrial prime mover. However, economic considerations based on the eiciency of the gas turbine dictate the use of a fuel for this purpose which is cheaper than diesel fuel; otherwise, other forms of power such as diesel engines become competitive with gas turbines.

lOne of the main problems arising in the use of residual fuel oils in gas turbines is the corrosiveness induced by those residual fuels containing sufficient amounts of vanadium to cause corrosion. Where no vanadium is present or the amount of vanadium is small, no appreciable corrosion is encountered. While many residual fuel oils as normally obtained in the refinery contain so little vanadium, or none, as to present no corrosion problems, such non-corrosive fuel oils are not always available at the point where the oil is to be used. In such instance, the cost of transportation of the non-corrosive oil to the point of use is often prohibitive, and the residual oil loses its competitive advantage. These factors appear to militate against the extensive use of residual fuel oils for gas turbines. Aside from corrosion, the formation of deposits upon the burning of a residual fuel in a gas turbine may result in unbalance of the turbine blades, clogging of openings and reduced thermal eliiciency of the turbine.

Substantially identical problems are encountered when using a solid residual petroleum fuel containing substantial amounts of vanadium. These fuels are petroleum residues obtained by known methods of petroleum rening such as deep vacuum reduction of asphaltic crudes to obtain solid residues, visbreaking of liquid distillation bottoms followed by distillation to obtain solid residues, coking of liquid distillation bottoms, and the like. The solid residues thus obtained are known variously as petroleum pitches or cokes and find use as fuels. Since the vanadium content of theoriginal crude oil tends to concentrate in the residual fractions, and since the processing of the residual fractions to solid residues results in further concentration of the vanadium in the solid residues, the vanadium corrosion problem tends to be intensified in using the solid residues as fuel.

The vanadium-containing ash present in the hot ue gas obtained from the burning of a residual fuel containing substantial amounts of vanadium compounds causes catastrophic corrosion of the turbine blades andA other metal parts in a gas turbine. The corrosive nature of .the ash appears to be due to its vanadium oxide content. Certain inorganic compounds of vanadium, such as vanadium oxide (V205), which are formed on combustion rates Patent of a residual fuel oil containing vanadium compounds, vigorously attack various metals, their alloys, and other materials at the elevated temperatures encountered in the combustion gases, the rate of attack becoming progressively more severe as the temperature isincreased. The vanadium-containing ash forms deposits on the parts af- `fected and corrosively reacts with them. It is a hard, adherent material when cooled to ordinary temperatures.

The economic factors involved preclude any extensive treatment of vanadium-containing residual fuels to remove the vandaum therefrom or to mitigate its effects. The vanadium compounds in residual oils are not removed by ceutrifuging or by the conventional chemical refining treatments.

It has now been discovered that residual petroleum fuels containing vanadium in an amount sufficient to yield a corrosive vanadium-containing ash upon combustion can be rendered substantially less corrosive, not withstanding the normally corrosive vanadium content, by incorporating therein a small amount, sufficient to retard the corrosiveness of the ash, of calcium hypochlorite. In the fuel compositions of the invention, corrosion due to the vanadium-containing ash is substantially retarded.

The single figure of the drawing shows an apparatus for testing the corrosivity of residual fuel oil compositions.

The type of residual fuel oils to which the invention isv directed is exemplified by No. 5, No. 6 and Bunker C fuel oils which contain a sufficient amount of vanadium to form a corrosive ash upon combustion. These are residual type fuel oils obtained from petroleum by methods known to the art. For example, residual fuel oils are obtained as liquid residua by the conventional distillation of total crudes, by atmospheric and vacuum reduction of total crudes, by the thermal cracking of topped crudes, by visbreaking heavy petroleum residua, and other conventional treatments of heavy petroleum oils. Residua thus obtained are sometimes diluted with distillate fuel oil stocks, known as cutter stocks, and the invention also includes residual fuel oils so obtained, provided that such oils contain suiiicient vanadium nor.- mally to exhibit the corrosion characteristics described herein. It should be understood that distillate fuel oils themselves contain either no vanadium or such small amounts as to present no corrosion problem. The total ash from commercial residual fuel oils usually ranges Afrom about 0.02 to 0.2 percent by weight. The vanadium pentoxide (V205) content of such ashes ranges from zero to trace amounts up to about 5 percent by weight for low vanadium stocks, exhibiting no significant vanadium corrosion problem, to as much as percent by weight for some of the high vanadium stocks, exhibiting severe corrosion.

The type of vanadium-containing solid residual fuels to which the invention is directed is exemplified by the coke obtained in known manner by the delayed thermal coking or fluidized coking of topped or reduced crude oils and by the pitches obtained in known manner by the deep vacuum reduction of asphaltic crudes to obtain solid residues. These materials have ash contents of the order of 0.18 percent by Weight, more or less, and contain corrosive amounts of vanadium when prepared from stocks containing substantial amounts of vanadium. A typical pitch exhibiting corrosive characteristics upon combustion had a softening point of 347 F. and a vanadium content, as vanadium, of 578 parts per million.

The corrosion retarding additive of the invention is, as has been stated, calcium hypochlorite. -In the practice of the invention with vanadium-containing residual fuel oils, `calcium hypochlorite .is uniformly blended with the oil in proportion to the vanadium content thereof. This is accomplished by suspending the finely-divided dry salt inthe oil or by Vemulsifying a water solution of the Vsalt in the oil. AIf desired, suitable surface active agents, such as .sorbitan monooleate and monolaurate and the ethylene oxide condensation products thereof, glycerol monooleate, and the like, which promote the stability ofthe suspensions or emulsions, can be employed.

In the practice of the invention, with the solid residual fuels, incorporation of calcium hypochlorite is accomplished in .several ways. The additive can be suspended or dispersed in the liquid vanadium-containing residual stocks or crude oil stocks from which the solid residual fuels of the invention are derived, and the mixture can then be subjected to the refining process which will produce the solid fuel. For example, in the production of a pitch by the deep vacuum reduction of an asphaltic crude oil, the additive is slurried with the oil in proportion to the vanadium content thereof, and the whole subjected to deep vacuum reduction to obtain a pitch containing uniformly dispersed therein the additive. As still another alternative, particularly with a pitch which is withdrawn in molten form from the processing vessel, the additive can be mixed with .the molten pitch and the mixture allowed to solidify after which it is ground to the desired size.

In the case of either liquid or solid residual fuels, the calcium hypoehlorite additive can be separately fed into the burner as the dry salt or an oil dispersion or water solution thereof. In any such case, it ispreferred to meter the additive into the fuel line just lprior to the combustion zone. ln a gas turbine plant where the heat resisting metallic parts are exposed to hot combustion gases at temperatures of the order of 1200" IF. and above, the additive can be added separately from the fuel either prior to or during combustion itself, or even subsequent to combustion. However it may specifically be added, whether in admixture with or separately from .the fuel, the additive `is introduced vinto said plant upstream of the heat resisting .metal parts to be protected from corrosion.

.The calcium hypochlorite additive is employed in a small amount with respect to the vanadium-containing residual fuel, sirliicient to retard the corrosiveness of the ash. Ordinarily, to achieve practical corrosion retardation, it is desirable to employ such an amount of additive as to result in at least about 1 atom weight of calcium per atom weight of the vanadium in the fuel. Preferably, the atom weight ratio, calcium to vanadium, is 3:1, although larger amounts of the additive, say 6:1 or even higher, can be employed.

The following specific examples are further illustrative of the invention.

EXAMPLE 1 Uniformly blend into a residual fuel oil having an ash content of 0.04 percent by weight, a sulfur content of 1.6 percent by weight, and containing 182 parts per million of vanadium and 2 parts per million of sodium, 0.27 percent by weight of calcium hypochlorite, U.S.P. The atom weight ratio, Ca:V, obtained is 6:1.

EXAMPLE 2 To a residual fuel oil having an ash content of 0.04 percent by weight, a sulfur content of 1.77 percent by weight, and containing 203 parts per million of vanadium and 1l parts per million of sodium, add and uniformly blend 0.16 percent by weight of the same calcium hypochlorite of Example l. An atom weight ratio, Ca:V, of 3:1 is obtained.

EXAMPLE 3 Repeat Example 2, except employ 0.08 percent by weight of the calcium hypochlorite, .All atom weight ratio, CazV, of 1.5:1 is obtained.

EXAMPLE 4 Melt a solid petroleum pitch obtained from the deep vacuum reduction of an asphaltic crude. This pitch has a softening point of 347 F. and a vanadium content of 578 parts per million. While the `pitch is in molten form, add and uniformly blend therein 0.54 percent by weight of calcium hypochlorite. Upon cooling and solidiication, grind the mixture to about 150 mesh. The resulting fuel has an atom weight ratio, CazV, of 3:1.

VIn order to test the effectiveness of the additives of this invention under conditions of burning residual fuels in a gas turbine, the apparatus shown in the drawing is employed. As shown in the drawing, the residual oil under test is introduced through line 10 into a heating coil 11 disposed in a tank of water 12 maintained at such temperature that the incoming fuel is preheated to a temperature of approximately 212?. From the heating coil 11 the preheated oil is passed into an atomizing head designated generally as 13. The preheated oil passes through a passageway 14 into a nozzle 15 which consists of a #26 hypodermic needle of approximately 0.008 inch LD. and 0.018 inch O.D. The tip of the nozzle is ground square and allowed to project slightly through an orifice 16 vof approximately 0.020 inch Vdiameter. The orice is supplied with 65 p.s.i.g. air for atomization of the fuel into the combustion chamber 21. The air is introduced through line 17, preheat coil 18 in tank 12, and air passageways 19 and 20 in the atomizing head 13. The combustion chamber 21 is made up of two concentric cylinders 22 and 23, respectively, welded to two end plates 24 and 25. Cylinder 22 has a diameter of 2 inches and cylinder 2'3 has a ldiameter of 3 inches; thelength of the cylinders between the end plates is 81/2 inches. End plate 24 has a central opening 26 into which the atomizing head is inserted. End plate 25 has a one (1) inch opening 27 covered by a baille plate 28 mounted in front of it to prevent direct blast of flame on the test specimen 29. Opening 27 in end plate 2S discharges into a smaller cylinder 30 having a diameter of 11/2 inches and a length of 6 inches. The specimen 29 is mounted near the downstream end of the cylinder approximately 1% inches from the outlet thereof. Combustion air isintroduced by means of air inlet 31 into the annulus between cylinders 22 and 23, thereby preheating the combustion air, and then through three pairs of 1716 inch tangential air inlets 32 in the inner cylinder 22. The first pair of air inlets are spaced 1A inch from end plate 24; the second pair 5% inch from the first; and the third 3 inches from the second. The additional heating required to bring the combustion products to test temperature is supplied by an electric heating coil 33 surrounding the outer cylinder 23. The entire combustion assembly is surrounded by suitable insulation 34. The test specimen 29 is a metal disc one inch in diameter by 0.125 inch thick, with a hole in the center by means of which the specimen is attached to a tube 35 containing thermocouples. The specimen and tube assembly are mounted on a suitable stand 36.

In conducting a test in the above-described apparatus, a weighed metal specimen is exposed to the combustion products of a residual fuel oil, the specimen being maintained at a selected test Atemperature of, for example, 1350, 1450 or 1550 F. by the heat of the combustion products. The test is usually run for a period of hours with the rate of fuel feed being 1/2 pound per hour and the rate of atomizing air feed being 2 pounds per hour. The combustion air entering through air inlet 31 is fed at 25 pounds per hour. At the end of the test run the specimen is reweighed to determine the weight of deposits and is then descaled with a conventional alkaline descaling salt in molten condition at 475 C. After descaling, the specimen is dipped in 6 N hydrochloric acid containing a conventional pickling inhibitor, and is theni washed, dried and weighed. The loss in Weight of the specimen 'after descaling is -the corrosion loss.

Tests are conducted in the apparatus just described using a 25-20 stainless steel as the test specimen. The tests are run for 100 hours at a temperature of 1450 F. under the conditions described above. Comparative tests are run with the uncompounded oils of Examples 1 and 2 and with the residual fuel compositions of Examples 1, 2 and 3. The test results are shown in the following table.

The tremendous .reduction in corrosion due to the use of the `additive is clear from the above table.

It has been found that the effectiveness of the additive of the invention is not only due to its calcium content 4but also to the nature of the other materials in the molecule. This is made clear when comparative tests are run with such inorganic prior art additives as calcium silicate, calcium oxide and calcium silicide. Thus tests are run under identical conditions, as Idescribed above for the results obtained in Table I, with the uncompounded oil of Example 1 and with the same oil containing calcium silicate, calcium oxide, calcium silicide and calcium hypochlorite, respectively. Each additive is employed in an amount su'icient to give an identical atom Weight ratio,

The outstanding superiority of the additive of the invention to the other calcium containing additives of the prior art is clear from the above table.

6 A typical analysis of the stainless steel employed in the above testing is shown in the following table in percent by weight:

Resort may be had to such modifications and variations as fall within the spirit of the invention `and the scope of the appended claims.

We claim:

1. A fuel composition comprising a major amount of a residual petroleum fuel yielding a corrosive Vanadiumcontaining ash upon combustion and a small amount of calcium hypochlorite in an amount suflcient to yield from about 1 to about 6 atom weights of calcium per atom Weight of vanadium in said fuel.

2.. The fuel composition of claim 1, wherein the fuel is a solid residual petroleum fuel.

3. A fuel composition comprising a residual petroleum fuel oil yielding a corrosive vanadium-containing ash upon combustion and an `amount of calcium hypochlorite sufficient to yield from about l to about 6 atom weights of calcium per atom weight of vanadium in said oil.

4. The fuel composition of claim 3, wherein the calcium hypoehlorite is employed in an amount sufficient to yield about 3 atom weights of calcium per atom weight of vanadium in said oil.

5. In a `gas turbine plant in which a fuel oil containing vanadium is burned and which includes heat resisting metallic parts exposed to hot combustion gases and liable to be corroded by the corrosive vanadium-containing ash resulting from the combustion of said oil, the method of reducing said corrosion which comprises introducing into said plant upstream of said parts a corrosion inhibiting amount of calcium hypochlorite, suiiicient to yield about 1 to about 6 atom weights of calcium per atom Weight of the vanadium in the fuel oil.

References Cited in the file of this patent FOREIGN PATENTS Great Britain Sept. 23, 1953 

5. IN A GAS TURBINE PLANT IN WHICH A FUEL OIL CONTAINING VANADIUM IS BURNED AND WHICH INCLUDES HEAT RESISTING METALLIC PARTS EXPOSED TO HOT COMBUSTION GASES AND LIABLE TO BE CORRODED BY THE CORROSIVE VANADIUM-CONTAINING ASH RESULTING FROM THE COMBUSTION OF SAID OIL, THE METHOD OF REDUCING SAID CORROSION WHICH COMPRISES INTRODUCING INTO SAID PLANT UPSTREAM OF SAID PARTS A CORROSION INHIBITING AMOUNT OF CALCIUM HYPOCHLORITE, SUFFICIENT TO YIELD ABOUT 1 TO ABOUT 6 ATOM WEIGHTS OF CALCIUM PER ATOM WEIGHT OF THE VANADIUM IN THE FUEL OIL. 